An offset printing unit has a plurality of rotatable cylinders, including a plate cylinder and a blanket cylinder. The plate cylinder carries a printing plate having a surface on which an inked image is defined. The blanket cylinder carries a printing blanket. The plate on the plate cylinder transfers the inked image to the blanket on the blanket cylinder at a nip between the plate cylinder and the blanket cylinder when the cylinders rotate. The blanket on the blanket cylinder subsequently transfers the inked image to the material being printed, such as a web of paper.
The printing plate transfers the inked image to the blanket upon each revolution of the plate cylinder and the blanket cylinder. A small amount of ink can remain on the surface of the blanket after the inked image is transferred from the blanket to the material being printed. If the printing plate transfers the inked image to the same location on the surface of the blanket upon each revolution of the cylinders, such small amounts of ink can build up at that location and can mar the printed image.